1. Field of the Invention
The present invention relates to porous material having hierarchical pore structure and preparation method thereof, and, more particularly, to a method of synthesizing a nanoporous material having high functionality as a support for bioactive material, which is newly combined with a three-dimensional rapid prototyping technique, thereby enabling practical application of a nanoporous material having hierarchical pore structure as a scaffold for tissue regeneration.
2. Description of the Related Art
In the medical field at present, regenerative medicine, which is receiving attention as a next-generation medical technique, in particular, medical treatment for artificially forming tissue by separating cells from tissue to be regenerated, culturing the cells, and inoculating the cells to an appropriate biomaterial to thus proliferate them, has raised a lot of interest. Such treatment requires a predetermined scaffold for supporting the cells to prevent the separation from connective tissue after implantation, and there is a need for the development of scaffolds having superior tissue compatibility and cell adhesion.
Conventionally, as the scaffold for supporting the cells, a polymer scaffold has been mainly used. To compensate for bone loss, a bone regeneration material includes calcium phosphate-based ceramic materials, including hydroxyapatite and tricalcium phosphate, and ceramic materials, including bioglass and calcium carbonate, having high mechanical strength and high bone compatibility. Furthermore, with the goal of serving as the bone regeneration material, a structure having three-dimensional pores is required. Methods of synthesizing a scaffold having three-dimensional pores include a preparation method (Korean Patent No. 10-331990) comprising preparing a fine ceramic powder slurry, applying the slurry on a polymer scaffold including polyurethane, and conducting heat treatment to remove polyurethane and to form a porous network, a preparation method using a multiple compression process (Byong-Taek Lee et al., Journal of the Korean Ceramic Society, 560, 41, 2004), a preparation method (Korean Unexamined Patent Publication No. 10-2003-0023568) through mutual contact of spherical ceramic particles, and a preparation method comprising mixing an organic material, such as polyvinylbutyral (Dean-Mo Liu, Biomaterials, 1955, 17, 1996) or methylcellulose (N. Ozgur Engin et al., Journal of the European Ceramic Society, 2569, 19, 1999), with slurry of fine ceramic powder. Although the scaffold thus obtained is composed of continuously connected macropores (having a size from ones to hundreds of micrometers), the structural control of the ceramic frames defining the pores is not conducted, and thus, although biocompatibility is exhibited, the functionality of the ceramic frame and histological osteoinduction are poor. Further, after the treatment, most of the scaffold has been confirmed to be separated from osseous tissue due to the intervention of connective tissue. Accordingly, there is required a biodegradable substitute material, which has superior biocompatibility and osteoinduction as well as osteoadhesion capabilities, may exhibit a predetermined function through the incorporation of a predetermined drug, and may be substituted into regenerative bone through appropriate absorption upon implantation.
If the ceramic frame of the three-dimensional scaffold defining macropores is composed of interconnected nanopores and semi-macropores, the specific surface and porosity are increased, and as well, cell adhesion is increased by the uneven surface. In the case where proliferation factors, nutrients, oxygen, or drugs are adsorbed into the nanopores, cell necrosis in the scaffold, which is regarded as the problem with a three-dimensional structure, may be expected to decrease, along with the improvement of cell proliferation and differentiation. Further, the scaffold is expected to act as a functional scaffold to regenerate bone and to heal inflammation through the adsorption of a drug, such as an anticancer agent or an anti-inflammatory agent.
As methods of synthesizing such nanopores, a polymer template method (C. T. Kresge et. al. 4, Nature, 710, 359, 1992), which facilitates the control of pore size or pore structure and also provides a giant specific surface area, is considered to be effective. The polymer template method is applied together with the above-mentioned three-dimensional scaffold synthesis technique, thereby making it possible to synthesize a scaffold having nanopores and macropores.
In addition, when two or three synthesis techniques, including the combination of the polymer template method and the three-dimensional scaffold synthesis technique, are applied together, the synthesis of a scaffold having hierarchical pores, including two kinds of pores of nano/macro size or three kinds of pores of nano/semi-macro/macro size, is expected to be enabled. Particularly, as a method of controlling the macropores, a typical three-dimensional rapid prototyping technique (Wai-Yee Yeong et al., Trends in Biotechnology, 643, 22, 2004) for forming a scaffold having a structure controlled in three dimensions using a polymer is applied, and consequently there are great expectations that a scaffold having a more controlled pore structure will be able to be synthesized.